Unexpected hope for millions as bleached coral reefs continue to supply nutritious seafood

Coral reef ecosystems support diverse small-scale fisheries -- and the fish they catch are rich in micronutrients vital to the health of millions of people in the tropics, a new Lancaster University-led study reveals.

And, counter-intuitively, following bleaching events that kill off coral and can transform the composition of reef ecosystems, reef fisheries can remain rich sources of micronutrients, even increasing in nutritional value for some minerals.

The findings, published today in the journal One Earth, show that the availability of micronutrients from coral reef small-scale fisheries may be more resilient to climate change than previously thought. This increased understanding is critical as continued global warming means coral bleaching events are becoming more frequent and more severe, placing greater stress on these vulnerable ecosystems.

Dr James Robinson, who led the study, said: "Our findings underline the continuing importance of these fisheries for vulnerable coastal communities, and the need to protect against over-fishing to ensure long-term sustainability of reef fisheries."

The researchers also caution that while these fisheries have proved more resilient to climate change disturbance than expected, continued understanding of the long-term impacts of climate change to coral reef fisheries, and more data from other regions, are urgent priorities.

More than six million people work in small-scale fisheries that rely on tropical coral reefs. Their catches help to feed hundreds of millions of coastal people in regions with high prevalence of malnourishment, causing stunting, wasting and anaemia. However, until now, the nutritional composition of coral reef fish catches, and how climate change might affect the nutrients available from reef fisheries, was not known.

This study, led by scientists from Lancaster University and involving an international team of researchers from the Seychelles, Australia, Canada and Mozambique, benefitted from more than 20 years of long-term monitoring data from the Seychelles, where tropical reefs were damaged by a large coral bleaching event in 1998, killing an estimated 90% of the corals.

Following the mass-bleaching event, around 60% of the coral reefs recovered to a coral-dominated system, but around 40% were transformed to reefs dominated by seaweeds. These differences provided a natural experiment for the scientists to compare the micronutrients available from fisheries on reefs with different climate-driven ecosystem compositions.

The scientists, who used a combination of experimental fishing, nutrient analysis, and visual surveys of fish communities in the Seychelles, calculated that reef fish are important sources of selenium and zinc, and contain levels of calcium, iron and omega-3 fatty acids comparable to other animal-based foods, such as chicken and pork.

They also found that iron and zinc are more concentrated in fish caught on reefs that have been transformed after coral bleaching and are now dominated by macroalgae such as Sargassum seaweeds. These seaweeds have high levels of minerals, which, researchers believe, is a key reason why the algal-feeding herbivorous fishes found in greater numbers on transformed reefs contain higher levels of iron and zinc.

Dr Robinson said: "Coral reef fish contain high levels of essential dietary nutrients such as iron and zinc, so contribute to healthy diets in places with high fish consumption. We found that some micronutrient-rich reef species become more abundant after coral bleaching, enabling fisheries to supply nutritious food despite climate change impacts. Protecting catches from these local food systems should be a food security priority."

The researchers believe the results underline the need for effective local management to protect the sustainability of reef fisheries, as well as policies that retain more of reef fish catches for local people and promote traditional fish-based diets. These can help reef fisheries to best contribute to healthy diets across the tropics.

Professor Christina Hicks, a co-author on the study, said: "Fish are now recognised as critical to alleviating malnutrition, particularly in the tropics where diets can lack up to 50% of the micronutrients needed for healthy growth. This work is promising because it suggests reef fisheries will continue to play a crucial role, even in the face of climate change, and highlights the vital importance of investing in sustainable fisheries management."

The study's authors include: James Robinson, Eva Maire, Nick Graham and Christina Hicks from Lancaster University; Nathalie Bodin from Seychelles Fishing Authority and Sustainable Ocean Seychelles; Tessa Hempson from James Cook University and Oceans Without Borders; Shaun Wilson from the Department of Biodiversity, Conservation and Attractions in Australia, and Oceans Institute, Australia; and Aaron MacNeil from Dalhousie University.